Abstract

The work reported in this thesis details the original research undertaken by the author into the cutting mechanics of wood-working handsaw tooth geometries. The research can be separated into three distinctive sections. The first section is a review of both fundamental and recent literature regarding wood characteristics and machining processes. The second section documents the findings of a cutting process in which a variety of work-piece parameters were evaluated whilst limiting the parameters associated with tooth geometry. The third and final section documents the findings of a cutting process in which a variety of tooth geometry parameters were evaluated whilst limiting work-piece variation.

Two separate experimental procedures were developed to carry out the work for sections two and three respectively: The first of these procedures utilised a CNC router machine to perform the controlled cutting action. A single “rip” tooth was attached to the tool holder. The workpiece was constrained to a tri-axis dynamometer which was used to measure the resultant tool forces in the relative X, Y and Z axes. At the same time a universal testing machine was employed to perform mechanical test procedures on a variety of wood species. A predictive cutting force model was developed using the obtained mechanical properties as categorical predictors.

The second procedure utilised a shaper machine to perform the controlled cutting action. Three different saw tooth geometries were evaluated for only one variety of wood species. A tri-axis dynamometer was again used to measure the resultant tool forces. The geometric parameters of each tooth were carefully evaluated at using SEM micrographs. A predictive cutting force model using the geometric parameters as categorical predictors was developed.

Chip and surface formation was carefully evaluated. For procedure one this involved observation of the chip/surfaces under an optical microscope. For procedure two this involved capturing footage of the cutting process using a high speed camera.

The findings of the research show that un-bevelled teeth with orthogonal edges generally yield high cutting forces. However, these teeth are very effective at removing material along the wood grain in a “chisel like” cutting action. Bevelled teeth with sharp lateral edges generally yield low cutting forces. These teeth are well suited to severing the wood fibres perpendicular to the grain in a “knife like” cutting action.